Conventionally a pattern shape of a semiconductor device is controlled in its manufacturing process using the dimensions such as a width of a line pattern or a diameter of a hole measured with a length-measuring SEM as means to evaluate a pattern formed as to whether it is formed as designed. Along with the miniaturization of semiconductor devices, it becomes common to form a pattern of the exposure wavelength or less, and to this end, ultra-high resolution techniques such as off-axis illumination and optical proximity correction are introduced. However, a change in pattern shape due to process fluctuations includes a tilt of a pattern side wall, rounding of a corner of a pattern or a constriction of a pattern, and deformation of a pattern due to a change in aberration of an exposure device, which are difficult to measure with the measurement of the pattern. Then, a technique to evaluate a tilt of a pattern side wall is known by creating outlines of an upper part and a lower part of a pattern side wall, and evaluating the tilt of the pattern side wall based on the two-dimensional shape of the pattern and the width of a white-band (see Patent Document 1).
This method enables the evaluation based on the two-dimensional shape of the pattern and the degree of tilt in the height direction of the pattern.
Projection exposure is a method to transfer a semiconductor pattern on a wafer, where light for exposure is applied to a photomask as a shielding member with a pattern to be printed drawn thereon, whereby an image of the photomask is projected on resist on the water through a lens system. During the exposure, the focus and the dose are determined as conditions of the exposure, and if the resist has unevenness at the surface due to nonuniformity of the resist application, the focus and the dose will be shifted, and so the dimensions and the shape of the pattern transferred may change, which is different from the normal pattern. The focus may be deviated due to other factors such as non-flatness resulting from a photomask and aberration of a lens.
Theses deviations in the focus and the dose resulting from the resist application, the photomask and the aberration of a lens have repeatability, and so a method of finding a correction value for the focusing and the dose with a semiconductor measurement device and feed-backing the correction value to an exposure device (see Patent Document 2) is known. This method can correct the deviation of focus and dose resulting from the resist application, the photomask and the aberration of a lens, whereby variations in dimensions of a pattern can be suppressed.
Aberrations of a lens include coma and astigmatism. Astigmatism causes a phenomenon where light is collected at different positions between in the horizontal direction and in the vertical direction. For instance, when a hole pattern is created by transferring a circle pattern having the same dimension for the horizontal and the vertical directions, astigmatism, if any, will cause an oval pattern having different dimensions between the horizontal and the vertical directions. To correct this, a method of finding a focus value using a line pattern (see Patent Document 2) is used, in which a focus value in the horizontal direction is found using a vertical line pattern and a focus value in the vertical direction is found using a horizontal line pattern, and correction is performed based on these focus values, whereby the optimum exposure conditions for the horizontal direction and the vertical direction can be obtained.
A focus value varies with unevenness of a wafer, and so it is better to know focus values for the horizontal and the vertical directions at one position. To this end, a method of using a dedicated pattern such as a cross pattern or a wedge-shaped pattern to obtain a vertical line pattern and a horizontal line pattern at one time also is available (see Patent Document 3).